Dr. Harding et al., OXIDATION PROTECTIVE BARRIER COATINGS FOR HIGH-TEMPERATURE POLYMER MATRIX COMPOSITES, Journal of materials research, 9(6), 1994, pp. 1583-1595
Three coating techniques (metal-organic chemical vapor deposition, mag
netron sputtering, and plasma-enhanced chemical vapor deposition) were
employed to deposit different coating materials (alumina, a superallo
y, and silicon nitride) on graphite-fiber-reinforced polyimide composi
tes to protect against oxidation at elevated temperatures. Adhesion an
d integrity of the coatings were evaluated by isothermal aging (371-de
grees-C for 500 h) and thermal cycling (25 to 232-degrees-C for 1000 c
ycles and -18 to 232-degrees-C for 300 cycles). Best results were achi
eved with a plasma-deposited, amorphous silicon nitride (a-SiN: H) coa
ting, which withstood stresses from 0.18 to -1.6 GPa. The major factor
s affecting the suitability of a-SiN: H as an oxidation protective coa
ting are the surface finish of the polymer composite and the presence
of a sizable hydrogen content in the coating.